Effect of maize root exudates on indole-3-acetic acid production by rice endophytic bacteria under influence of L-tryptophan

Abstract

Background: It is assumed that plant growth regulators produced by beneficial bacterial species could also influence plant growth. IAA is a major plant growth regulator responsible for stimulation of plant growth. There are several microorganisms which are naturally responsible for L- tryptophan metabolism. Methods: In total, 56 indigenous morphologically distinct isolates from rice roots were selected and subsequently characterized with biochemical tests, 16S rRNA sequencing and plant growth promoting activities. Pseudomonas fluorescens RE1 (GenBank: MF102882.1) and RE17 (GenBank: MF103672.1) endophytes resulted in better PGP activity against the other 54 isolates. Both endophytes were tested to screen indole-3-acetic acid production ability in pure culture conditions with L-tryptophan at 0, 50, 100, 200 and 500µg/ml concentrations. Results: P. fluorescens RE1 was recorded efficient for indole production in comparison to P. fluorescens RE17 at various L-tryptophan concentrations. P. fluorescens RE1 was shown to produce between 0.8 µg/ml and 11.5µg/ml of indole at various tryptophan concentrations, while RE17 produced between 1.2µg/ml and 10.2µg/ml. At 200 and 500µg/ml tryptophan concentration, P. fluorescens RE17 produced 7.4pmol/ml and 9.3pmol/ml IAA, respectively. Conclusions: Inoculation of maize seed with P. fluorescens RE1 and RE17 showed a significantly higher level of IAA production in comparison to non-inoculated seeds. Current study outcomes proved that plant growth regulators produced by Pseudomonas species could also play a critical role in plant growth promotion.

Halotolerant rhizobacteria Pseudomonas pseudoalcaligenes and Bacillus subtilis mediate systemic tolerance in hydroponically grown soybean (Glycine max L.) against salinity stress

“…The strains were identified using nearly complete sequence of 16S rRNA gene on Ez-Taxon (http://eztaxon-e.ezbiocloud.net). The phylogenetic tree was generated using the Phylogeny.fr platform and analysed using maximum-likelihood method implemented in the PhyML programme [21].…”

Assessment of plant growth-promoting stress-tolerant endophytes screened from Bougainvillea glabra for the growth of Triticum aestivum L. and Zea mays

“…The bacterial isolates (100 μl) were incubated in DF medium supplemented with L-tryptophan (10 g/l) for 48 h at 28 ± 1EC. The culture broth was centrifuged at 11963 g in a cooling centrifuge, and 1 ml of the culture supernatant was incubated with 2 ml of Salkowski reagent in a test tube (Karnwal and Dohroo, 2018). This mixture was left without any disturbance in the dark at room temperature for 30 min.…”

“…Production of IAA is one of the most critical traits of a wide variety of soil microorganisms used as plant growth promoters. IAA is a plant developmental hormone associated with rhizome propagation, plant cell proliferation, and cell duplication, and therefore, IAA biosynthetic activity of microorganisms is essential for plant development (Karnwal and Dohroo, 2018). Among all the reported auxins, IAA is the essential growth enhancer for plant root system development (Glick, 1995).…”

“…Several researchers (Tak et al, 2013;Kumar and Verma, 2018) have reported that the efficacy of plant growth-promoting rhizobacteria (PGPR) reduces under sudden changes of environmental conditions and they fail to respond in the field due to stress conditions. Therefore, selection for suitable stress-resistant species has become an essential parameter during the screening of microbial isolates suitable for the production of microbial inoculants (Karnwal and Dohroo, 2018). Salt stress in fields resulted in a significant decline of crop production for salt-susceptible and salt stress-tolerant plants.…”

Effect of Indigenous Rhizobacteria and Manure on the Growth and Yield of Red Potato (Solanum tuberosum L.) in Solok, West Sumatera

“…in corn stimulated IAA. IAA increased in leaf tissue and root [41] [42]. PGPR produced IAA, a hormone could induce plant resistant to pests and diseases.…”